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65816: improve decimal calculations, posted IO addresses, read/write during redundant read-modify-write cycle.

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This commit is contained in:
Thomas Harte 2022-06-21 14:33:06 -04:00
parent ec98736bd7
commit 7dcfa9eb65
3 changed files with 49 additions and 31 deletions
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71
Processors/65816/Implementation/65816Implementation.hpp
View File

@ -115,6 +115,13 @@ template <typename BusHandler, bool uses_ready_line> void Processor<BusHandler,
read(data_address_, data_buffer_.next_input());
break;
case CycleStoreOrFetchDataThrowaway:
if(registers_.emulation_flag) {
perform_bus(data_address_, data_buffer_.preview_output(), MOS6502Esque::InternalOperationWrite);
break;
}
[[fallthrough]];
case CycleFetchDataThrowaway:
perform_bus(data_address_, &bus_throwaway_, MOS6502Esque::InternalOperationRead);
break;
@ -141,10 +148,6 @@ template <typename BusHandler, bool uses_ready_line> void Processor<BusHandler,
write(data_address_, data_buffer_.next_output());
break;
case CycleStoreDataThrowaway:
perform_bus(data_address_, data_buffer_.preview_output(), MOS6502Esque::InternalOperationWrite);
break;
case CycleStoreIncrementData:
write(data_address_, data_buffer_.next_output());
increment_data_address();
@ -906,35 +909,43 @@ template <typename BusHandler, bool uses_ready_line> void Processor<BusHandler,
case SBC:
if(registers_.flags.decimal) {
// I've yet to manage to find a rational way to map this to an ADC,
// hence the yucky repetition of code here.
const uint16_t a = registers_.a.full & registers_.m_masks[1];
unsigned int result = 0;
unsigned int borrow = registers_.flags.carry ^ 1;
const uint16_t decimal_result = uint16_t(a - data_buffer_.value - borrow);
const uint16_t decimal_result = uint16_t(a - data_buffer_.value - (1 ^ registers_.flags.carry));
data_buffer_.value = ~data_buffer_.value & registers_.m_masks[1];
#define nibble(mask, adjustment, carry) \
result += (a & mask) - (data_buffer_.value & mask) - borrow; \
if(result > mask) result -= adjustment; \
borrow = (result > mask) ? carry : 0; \
result &= (carry - 1);
#define begin_nibble(mask) \
result += (a & mask) + (data_buffer_.value & mask);
#define end_nibble(adjustment, carry) \
if(result < carry) result -= adjustment; \
result &= (carry | (carry - 1));
#define nibble(mask, adjustment, carry) \
begin_nibble(mask); \
end_nibble(adjustment, carry)
unsigned int result = registers_.flags.carry;
nibble(0x000f, 0x0006, 0x00010);
nibble(0x00f0, 0x0060, 0x00100);
nibble(0x0f00, 0x0600, 0x01000);
nibble(0xf000, 0x6000, 0x10000);
begin_nibble(0xf000);
registers_.flags.overflow = uint8_t((( (decimal_result ^ result) & (~decimal_result ^ result) ) >> (1 + registers_.m_shift))&0x40);
end_nibble(0x6000, 0x10000);
#undef nibble
#undef begin_nibble
#undef end_nibble
registers_.flags.overflow = (( (decimal_result ^ a) & (~decimal_result ^ data_buffer_.value) ) >> (1 + registers_.m_shift))&0x40;
registers_.flags.set_nz(uint16_t(result), registers_.m_shift);
registers_.flags.carry = ((borrow >> 16)&1)^1;
registers_.flags.carry = (result >> (8 + registers_.m_shift))&1;
LDA(result);
break;
}
data_buffer_.value = ~data_buffer_.value & registers_.m_masks[1];
[[fallthrough]];
case ADC: {
@ -942,22 +953,28 @@ template <typename BusHandler, bool uses_ready_line> void Processor<BusHandler,
const uint16_t a = registers_.a.full & registers_.m_masks[1];
if(registers_.flags.decimal) {
uint16_t partials = 0;
#define begin_nibble(mask) \
result += (a & mask) + (data_buffer_.value & mask);
#define end_nibble(limit, adjustment, carry) \
if(result >= limit) result = ((result + adjustment) & (carry - 1)) + carry;
#define nibble(mask, limit, adjustment, carry) \
begin_nibble(mask); \
end_nibble(limit, adjustment, carry)
result = registers_.flags.carry;
#define nibble(mask, limit, adjustment, carry) \
result += (a & mask) + (data_buffer_.value & mask); \
partials += result & mask; \
if(result >= limit) result = ((result + (adjustment)) & (carry - 1)) + carry;
nibble(0x000f, 0x000a, 0x0006, 0x00010);
nibble(0x00f0, 0x00a0, 0x0060, 0x00100);
nibble(0x0f00, 0x0a00, 0x0600, 0x01000);
nibble(0xf000, 0xa000, 0x6000, 0x10000);
begin_nibble(0xf000);
registers_.flags.overflow = (( (uint16_t(result) ^ registers_.a.full) & (uint16_t(result) ^ data_buffer_.value) ) >> (1 + registers_.m_shift))&0x40;
end_nibble(0xa000, 0x6000, 0x10000);
#undef nibble
registers_.flags.overflow = (( (partials ^ registers_.a.full) & (partials ^ data_buffer_.value) ) >> (1 + registers_.m_shift))&0x40;
#undef begin_nibble
#undef end_nibble
} else {
result = int(a + data_buffer_.value + registers_.flags.carry);

4
Processors/65816/Implementation/65816Storage.cpp
View File

@ -195,8 +195,8 @@ struct CPU::WDC65816::ProcessorStorageConstructor {
if(!is8bit) target(CycleFetchIncrementData); // Data low.
target(CycleFetchData); // Data [high].
if(!is8bit) target(CycleFetchDataThrowaway); // 16-bit: reread final byte of data.
else target(CycleStoreDataThrowaway); // 8-bit rewrite final byte of data.
target(CycleStoreOrFetchDataThrowaway); // Native mode: reread final byte of data.
// Emulated mode: rewrite final byte of data.
target(OperationPerform); // Perform operation within the data buffer.

5
Processors/65816/Implementation/65816Storage.hpp
View File

@ -39,8 +39,9 @@ enum MicroOp: uint8_t {
/// Stores a byte from the data buffer.
CycleStoreData,
/// Stores the most recent byte placed into the data buffer without removing it.
CycleStoreDataThrowaway,
/// Emulated mode: stores the most recent byte placed into the data buffer without removing it;
/// Native mode: performs CycleFetchDataThrowaway.
CycleStoreOrFetchDataThrowaway,
/// Stores a byte to the data address from the data buffer and increments the data address.
CycleStoreIncrementData,
/// Stores a byte to the data address from the data buffer and decrements the data address.